feat(doctor): add per-fix confirmation mode (bd-3xl)

Add --interactive/-i flag to bd doctor --fix that prompts for each
fix individually. Users can approve/skip each fix with options:
[y]es, [n]o, [a]ll remaining, or [q]uit.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmd/bd/doctor_test.go

@@ -956,3 +956,18 @@ func TestCheckSyncBranchConfig(t *testing.T) {
 		})
 	}
 }
+
+// TestInteractiveFlagParsing verifies the --interactive flag is registered (bd-3xl)
+func TestInteractiveFlagParsing(t *testing.T) {
+	// Verify the flag exists and has the right short form
+	flag := doctorCmd.Flags().Lookup("interactive")
+	if flag == nil {
+		t.Fatal("--interactive flag not found")
+	}
+	if flag.Shorthand != "i" {
+		t.Errorf("Expected shorthand 'i', got %q", flag.Shorthand)
+	}
+	if flag.DefValue != "false" {
+		t.Errorf("Expected default value 'false', got %q", flag.DefValue)
+	}
+}